EXCITATION WAVELENGTH DEPENDENT RAMAN SPECTROSCOPY OF ARTERY

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The goal of this project is to compare the performance of 785 nm and 830 nm based Raman spectroscopy for quantitative analysis of artery. Silicon based charge coupled device (CCD) detectors have low dark current and high quantum efficiency in the short wavelength region offering shot noise limited detection. In addition, standard diode lasers, holographic notch filters, efficient spectrographs and filtered optical fiber probes are readily available for 785 nm laser excitaion, often at economical pricing compared to those used in 830 nm laser excited Raman spectroscopy. However, biological tissue exhibits marked fluorescence with short wavelength (for e.g. 785 nm) NIR stimulation. Our current research has found that the shot noise generated by the fluorescence background signal to be prohibitive to artery disease analysis using 785 nm-excited Raman spectroscopy. We have also shown that longer wavelength excitation indeed affords sufficient reduction in fluorescence background and thus reduced shot noise to overcome present detection equipment limitations. Thus, it was shown that 830nm wavelength excitation is an optimal compromise between currently available technology and practical fundamental limitations, in accord with our previous work.